8 June 2001

Study indicates CLA prevalence on the increase

By Marianne Curtis

RESULTS from a survey on the sheep disease caseous lymphadenitis (CLA) show that its prevalence is increasing. But advice on control remains problematic because it is difficult to diagnose and little is known about its spread.

The survey, conducted by Bristol University research vet Sarah Binns, involved 264 vets and 94 producers belonging to the Sheep Veterinary Society (SVS). Questionnaires were also sent to three breed societies.

Producers were asked whether and when they had seen abscesses on sheep and whether any had been diagnosed as CLA.

Of the SVS producers surveyed, 53 reported seeing abscesses in their sheep between 1990 and 1999. CLA was diagnosed for seven of these. During the same period, 18% of the 264 vets surveyed saw at least one case of CLA. Of the 414 breed society respondents, between 42% and 60% of producers reported abscesses.

"Abscesses and CLA were observed most commonly in summer and the number of producers reporting abscesses in sheep each year appeared to show a rising trend," said Dr Binns.

"However, because there is still much to learn about the disease, it is difficult to advise on control."

But sensible steps when shearing and dipping may help, she suggests. "Shearing licences, introduced because of foot-and-mouth, which require contractors to disinfect equipment between farms should also help reduce risk of CLA spread. However, the gathering process may lead to within-flock transmission when there are infected animals.

"These flocks should start by shearing or dipping youngest sheep, where prevalence should be less than in older sheep, moving through the age range where possible. Shear or dip infected sheep last and avoid lancing abscesses."

Purchasing breeding stock also carries a risk of introducing CLA to clean flocks, she adds. "Talk to owners and ask whether their sheep have had it. Although you should look out for scars and abscesses around necks, infected animals may have recovered and show no signs of CLA."

It is difficult to predict what effect F&M slaughterings will have on CLA incidence. "Some infected flocks may have been culled. However, when restocking begins, infected breeding stock may be more widely spread."

&#8226 Dr Binns is willing to accept and test samples from suspected CLA abscesses submitted by vets free of charge, so the only cost to producers would be the vet visit.

Many flocks currently live with the disease, but there is no room for complacency. Should the disease continue to spread, it could result in increasing numbers of carcass condemnations for cull ewes and lambs.

Dr Binns is keen to hear in confidence from producers who suspect CLA in their flocks to help with her research (078-8591 3612). &#42

CLA SURVEY

&#8226 Signs of increasing prevalence.

&#8226 Get a diagnosis.

&#8226 Minimise spread risks.